The manufacture of precision engineered machines such as jet engines requires that various metal component parts be hot worked by forging, extruding, rolling, or by similar processes. These processes entail rapidly applying high pressure by means of a metal die or other tool to the part being worked to induce a high strain rate. The tools are often made of various steels such as H13 type tool steel. The parts are typically fabricated from materials such as titanium alloys, nickel alloys, or stainless steels. To facilitate these processes, the part and the tool are coated with a lubricant which minimizes friction between the part and tool and prevents metal to metal contact.
One class of hot metal working lubricants which is widely used is glass lubricants. These lubricant comprise ground glass particles which are suspended in a carrier. Such lubricants are applied to the part to be worked to reduce friction and minimize metal to metal contact which results in damage to the tool and part. Examples of commercially available lubricants include GP-803 available from Graphite Products (Brookfield, Ohio) and Deltaglaze.TM. 13 and 17 available from Acheson Colloids (Port Huron, Mich.).
Despite the use of commercially available glass lubricants, some materials remain difficult to hot work, especially in precision or net forging operations. Titanium alloys in particular have proven troublesome. Due to their high strength, these alloys require extremely high pressures in order to be worked, resulting in high friction conditions which commercially available lubricants cannot obviate entirely. For example, forge loads of 500 tons to 2000 tons, which can result in surface pressures in excess of 100 tons per square inch or more, are typical. At these pressures, lubricants are subjected to high shear stresses and temperatures which cause them to lose their lubricating properties. The loss of lubricating properties is related to changes in viscosity, surface tension, density, and chemistry. Without adequate lubrication, metal tools wear rapidly and friction between the tool and part often ruptures the surface of the part. In addition, metal to metal contact occurring under these conditions can result in localized welding of the part to the tool, further damaging the part and tool. As a result, dies must be repaired or replaced frequently and parts can require extensive reworking.
Accordingly, much effort has been made in the past to develop lubricants which can reduce the friction between a tool and part in hot working operations which are carried out at extremely high pressures, but thus far has fallen short of meeting all of the objectives. Therefore, what is needed in this field is a lubricant which will be capable of operating at the extremely high pressures used to hot work titanium alloys and like materials.